The present invention relates to fusing systems, and more specifically, to fixing apparatii comprising fixing films useful for fusing a latent image in an electrostatographic, including digital, machine. In embodiments of the present invention, there are selected fixing films comprising a substrate which comprises a fabric material. In embodiments, an outer layer is positioned over the fibrous substrate. The outer layer comprises a polymer, preferably a fluoropolymer or silicone rubber. In embodiments, the present invention allows for the preparation and manufacture of fixing films with excellent and, in embodiments, superior mechanical properties including superior adhesion of the substrate to the outer layer(s) resulting in a decrease in the occurrence of delamination of the outer layer or layers from the substrate. Also, in embodiments, the films retain sufficient strength at high operating temperatures. The films are also relatively flexible to allow for use in a wide range of environments. In addition, the films allow for a decrease in the occurrence of hot offset, improvement in the image quality and permit a decrease in contamination of other xerographic components such as photoconductors.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which may be the photosensitive member itself or other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known and normally requires heating the toner image to a temperature of between about 90.degree. C. to about 200.degree. C. or higher depending upon the softening range of the particular resin used in the toner. It is undesirable, however, to increase the temperature of the substrate substantially higher than about 250.degree. C. because of the tendency of the substrate to discolor or convert into fire at such elevated temperatures, particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat may be applied by heating one or both of the rolls, plate members, or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time are provided. The balancing of these parameters to enable the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
It is important in the fusing process that minimal or no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there. The referred to "hot offset" occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser, and accordingly it is desired to provide a fusing surface which has a low surface energy to provide the necessary release. To ensure and maintain good release properties of the fuser, it has become customary to apply release agents to the fuser member during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils to prevent toner offset.
With the fixing apparatus using a thin film in pressure contact with a heater, the electric power consumption is small, and the warming-up period is significantly reduced or eliminated. In the film embodiments, it is necessary for the film material to comprise a material which is flexible, yet able to maintain its mechanical and electrical properties over a wide temperature range. Problems have resulted in that elastomer materials tend to lose about 70 to 90% of their mechanical strength at high operating temperatures, for example about 190.degree. C. In an attempt to solve the lack of strength problems, multiple layered film systems, for example from 2 to 5 layers, have been developed. However, problems with delamination have occurred with fusing or film systems, which include 2 or more layers, in that the outer surface tends to pull away from the substrate upon multiple revolutions of the belt or film substrate during the fusing process. In addition, processes for preparation of such multilayered fusing films have not been successful at forming uniform thicknesses of the outer layer(s) of the belt or film.
U.S. Pat. No. 5,345,300 discloses a fuser roller in contact with a pressure belt, wherein the pressure belt comprises a material which may be cloth-like.
Therefore, there exists an overall need for a fusing film which is flexible, yet able to maintain adequate mechanical and electrical properties over a wide temperature range. In addition, there exists a need for a fuser film in which the outer layer is sufficiently bonded to the substrate to aid in prevention of delamination of the outer layer from the substrate. Moreover, there exists a need for a fuser film which provides for good release properties and a decrease in the occurrence of hot offset.